An anisotropic bouncing universe in non-local gravity

We show that it is possible to realize a cosmological bouncing solution in an anisotropic but homogeneous Bianchi-I background in a class of non-local, infinite derivative theories of gravity. We show that the anisotropic shear grows slower than in general relativity during the contraction phase, peaks to a finite value at the bounce point, and then decreases as the universe asymptotes towards isotropy and homogeneity, and ultimately to de Sitter. Along with a cosmological constant, the matter sector required to drive such a bounce is found to consist of three components_radiation, stiff matter and k-matter (whose energy density decays like the inverse square of the average scale factor). Generically, k-matter exerts anisotropic pressures. We will test the bouncing solution in local and non-local gravity and show that in the latter case it is possible to simultaneously satisfy positivity of energy density and, at least in the late time de Sitter phase, avoid the introduction of propagating ghost/tachyonic modes.

Automated summary

The study explores the possibility of realizing a cosmological bouncing solution in a non-local gravity theory in an anisotropic but homogeneous background, showcasing the behavior of anisotropic shear and the matter components required for the bounce. It is found that k-matter exerts anisotropic pressures and the bouncing solution can satisfy positivity of energy density while avoiding ghost/tachyonic modes in the de Sitter phase in non-local gravity.